We propose to measure simultaneously from an in situ cat ileal loop the direction and extent of changes in the Starling forces of the intestine under a variety of physiological challenges to the intestinal system. The forces measured are capillary hydrostatic pressure, lymph and plasma colloid osmotic pressure, lymph flow, capillary filtration coefficient and interstitial fluid pressure (implanted capsule). Additional parameters that are measured are intestinal blood flow, arterial and venous pressures, changes in pH and hematocrit, and changes in the albumin to globulin ratios of both plasma and lymph fluid from the intestine. The alteration of these forces will be measured during perturbations in both arterial and venous pressure, during drug induced vasodilation, vasoconstriction and changes in capillary permeability, hemodilution resulting from fluid infusions (e.g., saline), glucose induced mucosal absorption and cholera toxin induced mucosal secretion.